The invention relates to a method for the production of glass-coated electronic components and the use of said method for the passivation of electronic components.
Electronic components store, consume or transfer electrical net power, inter alia as passive components, such as electrical resistances, capacitors or also coils. On the other hand, active electronic components are components which can add electrical net power to a signal. Active components are in particular semiconductors, such as diodes.
Diodes are semiconductor components in the field of electronics, characterised by their asymmetric characteristic current-voltage-curve which strongly depends on the current direction. Mainly, diodes are used for faradaic rectification of alternating currents.
Common diodes, in particular with small power, consist of a silicon chip which is pre-passivated at the periphery and has contact between an n- and a p-semiconductor, connections of copper cover wires respectively copper cover head pins and a glass tube which encapsulates the diode and the connection points. The contacting between the chip and the connections is effected by pressure which is maintained by the glass tube.
The term “passivation of electrical components” means, inter alia, the application of a mechanically stable layer onto the final components or their casings. In this case, the passivation protects the component from mechanical damaging and other detrimental influences, such as impurities, and due to the protection in particular further processing can be optimized. Usually, the passivation of the electric components is effected by an application of a glass through dropping or vapour deposition. Therefore, passivation is a mechanical protection of electric components, such as diodes and transistors, and, in addition, helps to stabilise the electrical properties. For example, often, the application of the passivation layer is the final coating step during the production of a semiconductor. In addition, for opto-electric components often a layer having low reflection is applied.
A passivation by glass is generally used for enhancing the quality and the reliability, inter alia, for many kinds of Si-semiconductor components, of bipolar ICs up to faradaic power rectification facilities.
Glass layers which have been melt on (or burned) provide the already above mentioned secure protection of the semiconductor surfaces from mechanical and chemical actions during both, the production and the use. Due to their barrier and partial getter effect, they can also positively influence the electrical function of the components (blocking voltage, blocking currents).
The thermal expansion of silicon is about 3.3×10−6/K, which is very low. Glasses having similar low thermal expansion have high viscosities and therewith melting temperatures which are so high that they can not be used as passivation glasses. Therefore, for passivation only special glasses with special properties are used. The glasses must have, inter alia, a very good expansion adjustment, a good electrical insulation and a dielectrical break-through resistance.
In most production technologies, the glass passivation is followed by chemical process steps, such as etching of contact windows and electrolytic application of contacts which are associated with an attack on the glass. There are high differences between the chemical stabilities of the passivation glasses and they have to be considered from case to case, when the glass type is selected.
In the prior art, there are known a lot of passivation standard glasses which have proved oneself during practical use.
Zinc borosilicate glasses have the highest sensitivity against the attack of all strong chemicals, such as acids and bases. Therefore, they are only used for vapour deposited contacts—apart from the sinter glass diode technology, wherein during the galvanic tinning of the connection wires also a noticeable removal of glass takes place.
Zero-current nickelization is a special exposure for the passivation glasses. Only lead borosilicate glasses having burning (melting) temperatures of higher than or equal to 700° C. can substantially withstand this procedure.
Normally, the passivation glasses are poor in alkali, since alkali ions, especially at higher temperatures, can diffuse from the glass, for example, into the chip and therewith can affect the functionality, for example of a diode. In addition, the glasses are sodium- and lithium-free, except from conventional impurities.
However, a disadvantage of the known passivation glasses is that they contain a high portion of lead oxide (PbO).
Chemically and electrically stable glasses of the system PbO—ZnO—SiO2—Al2O3—B2O3 are known from the state of the art [M. Shimbo, K. Furukawa, J. Ceram. Soc. Jpn. Inter. Ed. 96, 1988, p. 201-205] and are used in electronics, inter alia, also for the passivation of diodes. In this case, lead oxide as an ingredient causes an especially high electrical insulation in the glasses.
Since lead oxide is an environmentally harmful ingredient and legislation tends more and more to the prohibition of the use of this substance in electric and electronic apparatuses, there is a need for PbO free glasses which, inter alia, are suitable for the passivation of electric components, such as semiconductor components, as well as for the use in lead-free diodes.
By the simple substitution of one or more other ingredients which are sufficiently available for lead oxide, the economical reproduction of the desired technical glass properties which are influenced by PbO can not be achieved.